The seats for powered aircraft, such as airplanes, rotorcraft, in particular helicopters, or analogous powered aircraft, incorporate means for protecting a passenger sitting on the seat in the event of a crash. The term “passenger” should be understood as covering any person on board the aircraft, whether the pilot or a person being transported. Such protection means are commonly constituted by energy-absorber means that are adapted to compensate for the stresses to which the seat is subjected in the event of violent impacts and/or sudden deceleration, in particular in the event of a crash. More particularly, the seat is commonly organized to compensate for deformation of the floor of the aircraft, and to absorb the energy induced by the forces to which the aircraft is subjected overall in the event of a crash. In a common embodiment, the seat associates a stand and a bucket comprising a seat proper with a back extending up therefrom. The stand is anchored to the floor of the aircraft via foot members and it includes leg members that are secured to the foot members and that together carry the bucket. The connection between the bucket and the leg members is of the type using pins or analogous members, being implemented by means of bolts that are mounted to engage simultaneously in the seat back and in the leg members.
Directions and positions that are said to be “lateral” are those associated with the sides, that are said to be “longitudinal” are associated with the front and the rear, and that are said to be “transverse” or “vertical” should all be taken into consideration relative to the position of a passenger installed on the seat.
There then arises the general problem of arranging passenger protection means that are incorporated in the seat. It is necessary for the bucket to be firmly held on the stand under normal conditions of operation of the aircraft. The seat must be structured to be capable of compensating deformation of the floor and also to be capable of absorbing the energy induced by the forces to which the seat is generally subjected in the event of a crash because of the sudden change in the speed of the aircraft.
More particularly, in the event of the aircraft crashing, deformation of the floor causes the stand to be deformed, and more particularly its foot members. The seat must be structured so as to compensate the forces on the passenger as a result of geometrical deformation, it being commonly accepted by way of indication that such deformation is an angular deflection of not more than about ±10°. This angular offset is considered in particular on either side of the initial installation plane of the seat in the aircraft. In order to avoid making its structure more complex and in order to avoid increasing the size and the weight of the seat, such deformation of the floor is traditionally compensated by distorting the stand and/or by the bucket being flexible. Nevertheless, such arrangements are not satisfactory since their implementation is often evaluated empirically on the basis of tests carried out in a laboratory, to the detriment of any rigorous approach that would be preferable, given the requirements relating to protecting passengers. Such a procedure leads to organizing the seat in a manner that is specific to predetermined crash situations and to corresponding modes of deformation of the stand that are estimated as being probable. Nevertheless, in practice, the way a crash takes place is random and may give rise to unpredictable effects on the aircraft and on the conditions of stand deformation. It would appear to be desirable for the structure of the seat to be organized so as to enable the effects of stand deformation to be compensated regardless of the stresses to which the seat might be subjected in any kind of crash situation.
In the event of the aircraft being subjected to a sudden change in speed, and in particular to strong deceleration, the seat needs to be organized to protect the passenger from the effects of such a change in the speed of the aircraft. A specific mechanism is traditionally used in order to absorb the energy induced by the high forces to which the seat is subjected overall during a crash. This mechanism for absorbing the energy induced by a sudden change in the speed of the aircraft is in particular interposed between the stand and the bucket. For example, it is known to mount the bucket slidably on the leg members of the stand so that it can be moved under the effect of a force having at least one component oriented along the gravity axis and/or passing transversely through the floor of the aircraft. Such a sliding mount is implemented using bolts that engage the seat back of the bucket and that are suitable for traveling along respective members for guiding movement in translation, such as rails or slideways, forming parts of the leg members of the stand. The bolts are prevented from sliding along the leg members by deformable retaining means, such that under normal operating circumstances of the aircraft the bucket is held firmly, but the stresses that are induced on the aircraft in the event of a crash cause the retaining means holding the bucket to the stand to deform.
For further information about the technological environment of the present invention, reference may be made to the following documents: FR 2 683 191 (Israel Aircraft Industries Ltd.); DE 4 312 343 (Eurocopter D. GmbH); or EP 0 814 020 (Martin-Baker Aircraft Co. Ltd.).